Amine salts of trimetaphosphimic acid



M. NIELSEN 3,185,733 L AMINE SALTS 0F TRIME'IAPHOSPHIMIC ACID x Ori inalFil d o t. 17, 1 P01 NH CI g 9 957 Phcsphoniirilic Chloride CrudeMixture or separated frimer Water Potassium Water Ammonium AcetateAcetate Crude Tripotassium ii'i metaphosphimate Perchloric AcidTrimefaphosphimic'v acid (HOPONH) Crude Triammonium irimetaphosphimateKCI NaOH

:Trimetaphosphimic acid dihydrate Monosodium dihydrogenfrimetaphosphimote I Disodium monohydrogen irimetaphosphimafe l-Trisodium trimetaphosphimate Monosodium dihydrogen trimetaphosphimaieDisodium monohydrogen 1r imetaphosphimaie INVENTOR. Morris L. NielsenATTORNE Y United States Patent AMINE SALTS 0F TRIMETAPHGSPIEVHC AClDMorris L. Nielsen, Dayton, Ohio, assignor to Monsanto Company, acorporation of Delaware Original application Oct. 17, 1957, Ser. No.690,865, new

Patent No. 3,018,167, dated Jan. 23, 1962. Divided and this applicationFeb. 20, 1% Ser. No. 90,546

1 Claim. (Cl. 260-579) The present invention relates to new compositionsof matter containing phosphorus and nitrogen. The invention relatesparticularly to new types of phosphorus-nitrogen compounds and theirsalts including trimetaphosphirnates and tetrametaphosphimates.

It is an object of the invention to prepare new crystalline forms oftrimeta-phosphimic acid, (HOPONI-D and tetrametaphosphimic acid,(HOPONHh, and novel alkali metal, ammonium and amine salts of theseacids which are of utility in Various industrial applications. It isalso an object of the invention to prepare rust inhibitors containingamine salts of trimetaphosphimic acid and tetrarnetaphosphimic acid.

The novel phosphorus-nitrogen compounds of the present invention areprepared by first reacting phosphorus pentachloride and ammoniumchloride by intimately mixing the same and then heating the mixture to atemperature of from 100 C. to 200 C. The intermediate product thusobtained is a mixture of phosphonitrilic chlorides which can bedistilled to yield the trimeric phosphonitrilic chloride, boiling point356.5 C., as the principal product and the tetramer, boiling point 328.5C., as the secondary product.

Although it is possible to hydrolyze the trimeric chloride totrimetaphosphimic acid and the tetramer to tetrametaphosphimic acid,solely by the use of water, the hydrolysis products are usually composedof a heterogeneous treated with aqueous potassium acetate instoichiometric amount so as to form the tripotassium or thetetrapotassiurn salt of the corresponding acid. The salt is separatedfrom the by-product potassium chloride by filtration or other means. Thesalt is then treated with perchloric acid, which treatment liberates thefree trimetaor tetrametaphosphimic acid and precipitates the insolublepotassium perchlorate. Filtration is then employed to remove theinsoluble precipitate from the water solution of the respective acidshaving the formula:

(HOPONH)3 or (HOPONHL;

It will be evident from the above formula that the trimeta-phosphimicacid has three acidic hydrogen atoms, while the tetra acid has four suchacidic hydrogen atoms. Any one or all of these acidic hydrogen atoms maybe neutralized by means of bases such as alkali metal or ammoniumhydroxides, carbonates, bicarbonates, etc., thus forming the triortetra-alkali metal salts, the ammonium salts or other salts having fewerthan all of the acidic hydrogen atoms neutralized. An important featureof our invention is the formation of various amine salts of these acidsas will be further described.

Instead of neutralizing all or part of the hydrogen atoms in theseacids, I may by ordinary concentration or 3,185,?33 Patented May 25,1965 evaporation obtain the respective triand tetra-phosphimic acids inpure anhydrous crystalline form.

The acids and salts contemplated in the present invention may bedesignated by the general formula,

M H (OPONH) z in which x is an integer from O to 4, y is an integer fromzero to 4, z is an integer from 3 to 4. M represents a univalent radicalselected from the group consisting of sodium, potassium, ammonium andhalf-amine radicals. The various salts of the present invention may alsobe prepared in hydrated form having from 1 to 7 moles of water per moleof the salt. When reference is made to the various salts, it is alsointended to include the respective hydrates thereof.

These acids of the present invention may be prepared in the form oftheir respective hydrates, such as the dihydrates. In order to preparesuch dihydrates the anhydrous acid is dissolved in water at roomtemperature, and alcohol is added, whereupon the dihydrate is thrown outof solution in the form of needle-like crystals.

The above process applicable either to trior tetrametaphosphimates isshown in schematic form in the drawing which is part of the presentspecification. In the flow sheet set forth in the drawing the startingmaterials are phosphorus pentachloride and ammonium chloride. These arereacted to give a crude mixture of phos phonitriiic chlorides composedpredominantly of the trimer with minor proportions of the tetramer ofphos phonitrilic chloride. The crude mixture of these chlorides, or adistilled fraction thereof, is then hydrolyzed by intimate admixture andreaction with Water and potas sium acetate. This results in theformation of a crude tripotassium trimetaphosphimate to obtain thedesired trimetaphosphimic acid while at the same time precipitatingpotassium chloride.

The trimetaphosphimic acid may then be separated from the aqueoussolution in which it is obtained at this point. Concentration of theaqueous solution by the evaporation of water yields the anhydrous acid,while precipitation from the aqueous solution, such as by the additionof a non-solvent, for example alcohol, results in the production of ahydrate of the acid, e.g., trimetaphosphimic acid dihydrate.

The flow sheet further indicates that salts of trimetaphosphimic acid,for example the sodium salt, may be obtained by reaction with thestoichiometric proportion of sodium hydroxide in order to obtain any ofthe three possible salts; monosodium dihydrogen trimetaphosphimate,disodium monohydrogen trimetaphosphimate or trisodiumtrimetaphosphirnate. The more highly alkaline salts may also be furtherreacted with the trimetaphosphimic acid as shown in the drawing. Forexample, either disodium monohydrogen trimetaphosphimate or trisodiumtrimetaphosphimate when reacted with additional trimetaphosphimic acidyields monosodium dihydrogen trimetaphosphimate. In the same manner,trisodium trimetaphosphimate when reacted with 0.5 mole oftrimetaphosphimic acid yields disodium monohydrogen trimetaphosphimate.

The flow sheet also shows a method for the production of triammoniumtrimetaphosphimate which is advantageously employed in a crude form as afertilizer component. An advantage of this compound as a fertilizermaterial is that the single compound supplies highly concentratedproportions of nitrogen and of phosphorus. In order to obtain thetriammonium trimetaphosphimate, the crude mixture of phosphonitrilicchloride, or if desired, particular distilled fractions, is hydrolyzedby intimately mixing said phosphonitrilic chloride with ammo niumacetate and water, thereby obtaining the crude triamrnoniumtrimetaphosphimate.

It is an advantage of the present process that the potassium, sodium,and ammonium salts of trimetaphosphimic acid and tetrametaphosphimicacid can be manufactured in very pure form. It has been found that theseparation process based upon the use of perchloric acid enables thisresult to be accomplished, while at the same time avoiding theproduction of undesirable hydrolysis products. in this method,fractional distillation of the original mixture of phosphonitrilicchlorides gives a narrow cut of starting material. The use of such afraction makes it possible to direct the reaction to the substantialexclusion of higher species with the result that the compounds obtainedare substantially pure salts of trimetaphosphimic acid or oftetrametaphosphimic acid. The fraction of phosphonitrilic chloride isreacted with a stoichiometric proportion of potassium acetate in thepresence of water using an organic solvent, such as ether for the saidphosphonitrilic chloride. The co-formed potassium chloride may beremoved by crystallization or ex traction wtih a suitable solvent.Metathesis of the potassium salt with perchloric acid results in theproduction of insoluble potassium perchlorate which is readily removedfrom the solution by filtration. The resultant solution consists ofpredominantly of trimetaphosphimic acid or tetrametaphosphimic acid inwater. The acid solution is concentrated by evaporating excess water,after which the crystalline acid is obtained by precipitation from thechilled solution. The pure trimetaphosphimic or tetrametaphosphimic acidmay then be transformed into the mono-, di-, or tri-salts of sodium,potassium, or ammoniurn by stoichiometric neutralization with thedesired basic material, for example, sodium hydroxide, sodium carbonate,potassium hydroxide or potassium carbonate. Ammonia may also be employedin either gaseous form or aqueous solution. In addition, higher alkalinesalts, such as the trisodium salt may be reacted with the free acid toyield the monoor dlSOdlUl'll salts of trimetaphosphimic acids.

The desired salt is then preferably precipitated with a non-solvent suchas alcohol or acetate. If desired, the salts may be crystallized fromthe saturated solution by evaporating and/or cooling.

The class of amine salts of trimetaphosphimic acid andtetrametaphosphimic acid are prepared by direct stoichiometricneutralization of the acid, such as by the use of an acetic acidsolution of o-tolidine which is mixed with the trimetaphosphimic acid orits salts in order to obtain the o-tolidine salt. The same method isapplicable to tetrametaphosphimic acid in order to obtain thecorresponding amine salts. The amines which may be employed includeethylenediamine; m-phenylenediamine; p-phenylenediamine; naphthidene;{3-naphthylamine; 4,4- diaminodibenzyl; 4,4-diaminostilbene and4,4'-diaminotolane. A preferred group of amines are benzidine,o-tolidine, o-dianisidine, monoalkyl and dialkylbenzidines. In thepresent group of amine salts, the amines are combined with the said acidmoiety, (HOPONH) and (HOPONH) respectively, in the proportion of fourhalf-amine radicals to one acid moiety.

The amine salts of trimetaphosphimic acid and the tetrametphosphimic.acid are generally insoluble in Water but are soluble in moltenacetamide, formamide and urea. The reaction which the salts have inwater upon prolonged contact is one of substantial neutrality.

The amine salts of trimetaphosphimic acid, for example, the o-tolidineor benzidine salts, are water-insoluble materials which decompose uponheating to release ammonia or free amines. These amine salts may beutilized as antioxidants, which are of particular utility in rubber,lubricating oil, and in antifreeze compositions. The amine salts mayalso be employed as biocides, for example, as a component of a shipsbottom paint in order to prevent the growth of barnacles. The aminesalts also have utility as indicators in a test for free halogen,

for example, chlorine. For example, the o-tolidine salt oftrimetaphosphimic acid turns from white to dark blue in the presence offree chlorine, bromine, or iodine.

Another field of utility for the amine salts of trimetaphosphimic acidand tetrametaphosphimic acid is as a corrosion inhibitor for steel andother ferrous metals. For this purpose, the said amine salts may beemployed in a wateror oil-base paint which is applied to the steel oriron surfaces. However, the amine salts may also be employed ascorrosion inhibitors in aqueous solutions by suspension in aqueoussolution, for example, as a minor component in a cooling water systemwhich must be circulated through the cast iron jacket of an internalcombustion engine to cool the engine. The hot water from the engine isthen cooled in a heat exchanger or cooling tower in which the water issubjected to an aeration treatment. In this relationship, the amine saltalso serves to reduce bacteria and algae growth in the system.

The salts such as monoand disodium, as well as the correspondingphosphorus salts of triand tetrametaphosphimic acid, are water-solublematerials which possess leavening activity. These compounds maytherefore be formulated with sodium bicarbonate to give a controlleddegree of leavening activity for use in baking. These salts are alsouseful as blowing agents which release ammonia or an amine as well asphosphorus acids in the manufacture of foamed plastics.

Another use for the present salts is as an acid reacting catalyst in thecondensation of urea-formaldehyde and melamine-formaldehyde resins.

The trimetaphosphimic acid in crystalline form as obtained by the methodof the present invention may be utilized as a fire-retardant agent whichcan be applied directly or from the solution to cellulose material, suchas cotton cloth in order to render the cloth resistant against thepropagation of a flame.

The acid may also be employed as a soldering flux since the acid, bothin the anhydrous or hydrated form, exists in a solid form which isstable at relatively high temperatures, but decomposes at about 200 C.with the release of phosphoric acid which cleans the metallic surface tobe soldered. The acid, particularly in the anhydrous form, is also ofutility as a dehydrating agent, and as an alkylating agent in variouschemical reactions.

The above discussion has been directed primarily towards the productionof highly pure forms of trimetaphosphirnic acid, tetrametaphosphimicacid and their salts. However, it is often desirable in the manufactureof fertilizer components to use a technical grade of these products. Thepresent invention therefore also contemplates the use of crude or lesshighly refined distilled trimer and tetramer mixtures of phosphonitrilicchloride, including various proportions of mixtures of the trimer andtetramer. In order to make use of such crude mixtures, the hydrolysisreaction is conducted with the stoichiometric amount of the alkali metalor ammonium acetate in water with the consequent production of thecorresponding salts. The alkali metal or ammonium trimetaphosphimate andthe co-formed tetrametaphosphimate salts thus obtained are particularlyuseful in fertilizers. For example, the potassium salts provide thethree essential elements, e.g., phosphorus, nitrogen and potassium in asingle chemical compound, which therefore aids in the formulation offertilizers for specific crops.

The following examples illustrate specific embodiments of the presentinvention.

Example 1 The tripotassium salt of trimetaphosphimic acid was preparedby first carrying out the hydrolysis of trimeric phosphonitrilicchloride in the presence of potassium acetate. Twelve grams of (trimericphosphonitrilic chloride was dissolved in ml. of water and the solutionstirred vigorously together with a solution of 60 grams of anhydrouspotassium acetate in 30 ml. of water for a' period of 50 hours. Thesolid product was then filtered oh and was purified by dissolving thesame in a minimum quantity of water and precipitating with alcohol. Thisrecrystallization was repeated until the solid product was free ofpotassium chloride. The yield was 4.5 g. of a product which uponanalysis was found to correspond to the formula K (OPONH) and having theanalysis: 11.71% N (11.96% calcd.), 26.26% P (26.45% calcd.), and 31.3%K (33.4% calcd.).

Example 2 Trimetaphosphimic acid was prepared in pure crystalline formas follows: To a solution of 4.5 g. of tripotassium trimetaphosphimatein 12.5 ml. of ice-cold water, there was slowly added 6.0 ml. of 72%perchloric acid. The precipitated potassium perchlorate was removed byfiltration after which the residual solution was evaporated to drynessunder vacuum while maintaining the temperature at below 35 C. Theprecipitated solids were washed with a mixture of ethyl acetate andmethanol (80:20 proportions by volume) to remove traces of potassiumperchlorate leaving 3 g. of pure anhydrous trimetaphosphimic acid.Analysis showed the compound to be H (OPONH) having 17.9% N (17.73%calcd.). The anhydrous acid crystallized as monoclinic platelets. TheX-ray diffraction analysis of the anhydrous acid showed the material tobe characterized by interplanar distances for the 3 strongest lines asfollows: 6.41; 3.31; and 6.11 Angstroms. The acid equivalentdetermination gave 79 (79 calcd.).

The trimetaphosphimic acid was also prepared as the dihydrate bydissolving the anhydrous acid described above in the minimum quantity ofwater at room temperature, and then adding hexane and alcohol toprecipitate needlelike crystals. In contrast to the anhydrous crystalswhich decomposed at about 150 C., the hydrated form was found to melt at110 C. Analysis showed the compound to be H (OPONH) -2H O having 15.40%N (15.9% calcd.) and 33.89% P (34.03% calcd.). The needle-like crystalsof trimetaphosphimic dihydrate were subjected to X-ray diffractionanalysis and were found to be characterized by interplanar distances asfollows for the 3 strongest lines: 5.44; 4.65; and 6.97 Angstroms. Theacid equivalent determined for the dihydrate was 91 (91 calcd.).

Example 3 Monosodium dihydrogen trimetaphosphimate was made by partialneutralization of the anhydrous trimetaphosphimic acid with trisodiumtrimetaphosphimate (previously obtained by the direct stoichiometricneutralization of the free acid with sodium hydroxide), in accordancewith the equation 2H (OPONH) +Na (OPONH) ZNaH (OPONH 3 The preparationwas carried out by dissolving 3.6 g. of trimetaphosphimic acid in 30 ml.of water. To this solution there was then added 2.84 g. of trisodiumtrimetaphosphimate. The solution was evaporated under vacuum at amaximum temperature of 35 C. yielding a crop of crystals weighing 6.6 g.Analysis of the product showed the compound to be NaH (OPONH) -2H Ocontaining 14.20% N (14.24% calcd.), 31.37% P (31.50% calcd.), and 7.7%Na (7.8% calcd.).

Example 4 Disodium monohydrogen trimetaphosphimate was made by partialneutralization of the free acid with sodium hydroxide. To a solution of1.18 g. of trimeric acid in 3 ml. of water there was added 0.4 g. ofsodium hydroxide dissolved in 2 ml. of water. The solution wasevaporated under vacuum at a maximum temperature of 35 C. until a thickpaste was obtained. This was then treated with methanol to precipitateneedle-shaped crystals which were 6 recovered by filtration giving ayield of 1.40 g. Analysis showed the compound to be Na H(OPONH) -2.5H Ohaving the elementary analysis of 12.86% N (12.95% calcd.), 28.38% P(28.52% calcd.), and 14.5% Na (14.1% calcd.).

Example 5 The production of the ammonium salt of trimetaphosphimic acidwas conducted by beginning with a crude mixture of the polymers ofphosphonitrilic chloride which had been obtained by heating a mixture ofPC1 and NH Cl to a temperature of from C. to 200 C. It was found thatthe mixture of polymeric phosphinitrilic chloride could be distilled toobtain a substantially pure fraction of the trimeric and tetrameric formof the chloride. Twelve grams of the trimeric phosphonitrilic chlo ridewas dissolved in ml. of water and the solution stirred vigorously with asolution of 50 g. of ammonium acetate in 40 ml. of water for a period of50 hours. The solid product which formed was filtered off and was thenpurified by dissolving the same in a minimum quantity of water andprecipitating the triammonium salt of trimetaphosphimic acid withalcohol. This precipitation was repeated until the solid product wasfree of ammonium chloride. The yield was 4.5 g. of product which uponanalysis was found to corespond to the formula and to have the analysis:27.19% N (27.46% calcd.), 29.40% P (30.36% calcd.).

The corresponding ammonium salt of tetrametaphosphimic acid was found tocorrespond to the formula (NH (OPONH) -4H O and to have the analyysis:24.55% N (24.56% calcd.), 26.95% P (27.16% calcd.).

Example 6 The amine salts of trimetaphosphimic acid andtetrametaphosphimic acid were prepared by employing 1% solutions of therespective amine dissolved in acetic acid. This solution was prepared bydissolving 0.1 g. of the recrystallized base, for example, o-tolidine in3.3 m1. of glacial acetic acid to which 6.7 ml. of water was added. Tothe above solution, there was then added, by dropwise addition, anaqueous solution of the trimetaphosphimic acid or tetrametaphosphimicacid or the sodium salts thereof (10% by weight solution in water) untilthe mixture became turbid. The amine salt was then observed to settleout and was completely removed by filtration. The amine salts were allfound to be white crystalline solids. The properties of the variousamine salts thus obtained are summarized below:

Interplanar distances of Example 7 The utility of the o-tolidine salt oftrimetaphosphimic acid as a corrosion inhibitor was demonstrated bypreparing a series of suspensions respectively containing: I, 2%; II,0.5%; III, 0.1% by weight of the o-tolidine salt of trimetaphosphimicacid. Another solution, IV, containing only water was employed as acontrol in the tests. The four solutions were placed in test tubes intowhich small polished samples of mild steel were placed. It was observedthat at the end of 24 hours the three solutions, I, II, and HI,containing the amine salt of trimetaphos phimic acid exhibitedsubstantially no rusting of the steel,

while the control solution, IV showed substantial rusting of thespecimen.

In general it has been found that aqueous or organic solutions ordispersion containing from 0.01% to 5% by weight of the amine salt, areuseful for corrosion inhibition.

The present patent application is a division of copending patentapplication, Serial No. 690,865, filed October 17, 1957 (now US. PatentNo. 3,918,167).

What is claimed is: The o-tolidine salt of trimetaphosphimic acid.

References Cited by the Examiner Stokes: American Chemical Journal, vol.18, 1896, pages 633 and 781.

CHARLES B. PARKER, Primary Examiner. IRVING MARCUS, Examiner.

